Heater control for an air dryer

ABSTRACT

An air dryer having a heater element associated with its valves to prevent freezing at cold temperatures. The air dryer includes a temperature sensor and an electronic controller that reads the temperature sensor and inhibits actuation of the valves whenever the temperature of valves is below freezing or a predetermined temperature that indicates a risk for freezing until the valves have been sufficiently warmed by the heater to avoid freezing during operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/865,781, filed on Sep. 25, 2015.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to railway air system air dryers and, moreparticularly, to an air dryer having a heating control system forpreventing freezing of valves.

2. Description of the Related Art

A typical “twin-tower” desiccant-type air dryer includes two dryingcircuits that are controlled by valves. Wet inlet air flows through onecircuit to remove water vapor, while dry product air counter flowsthrough the other circuit to remove the accumulated water and regeneratethe desiccant. Inlet and outlet valves for each pneumatic circuit areresponsive to controlling electronics to switch the air flow between thetwo circuits so that one circuit is always drying while the other isregenerating. The air dryer may include a pre-filtration stage with awater separator and/or coalescer positioned upstream of the dryingcircuits. The pre-filtration stage removes liquid phase and aerosolwater and oil that can accumulate in air supply system as a result ofthe compression of ambient air by the locomotive air compressors. Apre-filtration stage includes a drain valve that is used to periodicallypurge any accumulated liquid. For example, a typical pre-filtrationdrain valve actuation cycle might command a purge (open) for two secondsevery two minutes.

The air dryer valves, including any pre-filtration drain valve, areconstantly subjected to wet air and thus prone to freezing at lowtemperatures. In order to counteract this problem, a heater element maybe provided to warm the valves sufficiently to prevent freezing.Unfortunately, it takes time to sufficiently warm the valves when theair supply system is powered up from a cold temperature. If any of thevalves are commanded open before they are sufficiently warmed, thevalves can freeze in the open position. If a valve remains in an openposition when it should otherwise be closed, there is a risk of anuncontrollable venting of the compressed air from the locomotive airsupply system. Further, due to the high volume of air flowing throughthe frozen valve, the heater may not have sufficient power to thaw thefrozen valve, if it is frozen open. Thus, there is a need for a heatingcontrol system that ensures that the valves are sufficiently warmedbefore they are operated so that they do not freeze.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises an air dryer having an inlet forreceiving compressed air, a series of valves positioned in a valve blockfor controlling the movement of the compressed air through a desiccant,a heater configured to warm the valve block, a temperature sensor foroutputting a signal indicating the temperature of at least a portion ofthe air dryer, and a controller piloting the series of valves. Toprevent a risk of the valves freezing when operated, the controller isprogrammed to inhibit operation of the series of valves until the signalreceived from the temperature sensor indicates that the series of valvesare warm enough that they will not freeze when operated. The series ofvalves may include a pair of inlet valves and a pair of exhaust valvesassociated with a twin-tower desiccant air dryer. The series of valvesmay also include a drain valve associated with a pre-filtration stage.The temperature sensor is preferably positioned to determine thetemperature of air flowing through the air dryer, but may be installedin the valve block or positioned to detect the outside temperature.

The present invention also comprises a method of preventing frozen airdryer valves that involves the use of an air dryer comprising an inletfor receiving compressed air, a series of valves positioned in a valveblock for controlling the movement of the compressed air through adesiccant, a heater configured to warm the valve block, a temperaturesensor for outputting a signal indicating the temperature of at least aportion of the air dryer, a controller piloting the series of valves.The signal indicating the temperature in the air dryer is received bythe controller from the temperature sensor, and then the controllerinhibits operation of the series of valves if the signal received fromthe temperature sensor indicates that any of the series of valves couldfreeze when operated.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The present invention will be more fully understood and appreciated byreading the following Detailed Description in conjunction with theaccompanying drawings, in which:

FIG. 1 is a schematic of a locomotive air supply system having an airdryer having a heated valve block according to the present invention;

FIG. 2 is a schematic of an air dryer with integral pre-filtration stageand a heated valve block according to the present invention;

FIG. 3 is a schematic of a heated valve block of an air dryer withpre-filtration state according to the present invention; and

FIG. 4 is a flowchart of a heater control process for an air dryerhaving a heated valve block.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein like reference numerals refer tolike parts throughout, there is seen in FIG. 1 a locomotive air system10 having an air compressor 12, aftercooler 14, first and second mainreservoirs MR1 and MR2, and a two-tower desiccant air dryer 16 havingheater control according to the present invention, as more fullydescribed below. Second main reservoir MR2 is coupled to the brakingsystem 18 and a check valve 20 is positioned between the first andsecond main reservoirs MR1 and MR2. A pre-filtration stage 22 isassociated with air dryer 16 and includes a drain valve 24 that isoperated according to a drain valve purge cycle time.

Referring to FIG. 2, two-tower desiccant air dryer 16 comprises an inlet28 for receiving air from first main reservoir MR1. Inlet 28 is incommunication with pre-filtration stage 30, shown as comprising a waterseparator 32, a coarse coalescer 34, and a fine coalescer 36. Anyaccumulated liquids in water separator 32, coarse coalescer 34, and finecoalescer 36 are expelled through drain valve 24. A pair of inlet valves42 and 44 are positioned downstream of pre-filtration stage 30 fordiverting incoming air between one of two pathways, each of which isassociated with one of two desiccant towers 46 and 48. A temperaturesensor 50 is positioned upstream of inlet valves 42 and 44 anddownstream of pre-filtration stage 30. Optionally, the temperature, or asecond temperature sensor may be located in the valve block housing theseries of valves. The first pathway downstream of first inlet valve 42leads to an exhaust valve 52 and first desiccant tower 46. The secondpathway downstream of second inlet valve 44 leads to a second exhaustvalve 54 and second desiccant tower 48. The first pathway furtherincludes a first check valve 58 and first bypass orifice 62 downstreamof first desiccant tower 46, and the second pathway further includes asecond check valve 60 and bypass orifice 64 downstream of seconddesiccant tower 48. A single outlet 66 is coupled to the end of thefirst and second pathways, and a humidity sensor 68 is positionedupstream of outlet 66. Inlet valves 42 and 44 and outlet valves 52 and54 are piloted by controller 40. Controller 40 operates inlet valves 42and 44 and outlet valves 52 and 54 so that compressed air provided atinlet 28 is directed through one of desiccant towers 46 or 48 fordrying. The other of desiccant towers 46 or 28 may be regenerated byallowing dried air to reflow through bypass orifice 62 or 64 and out ofexhaust valve 52 or 54 as needed. Controller 40 is also in communicationwith temperature sensor 50 and humidity sensor 68. A heating element 70may also be coupled to controller 40 and positioned in air dryer 16 towarm drain valve 24, inlet valves 42 and 44 and outlet valves 52 and 54if the temperature is below freezing.

As seen in FIG. 3, the air dryer pathways seen in FIG. 1 are arranged sothat drain valve 24, inlet valves 42 and 44, and outlet valves 52 and 54are commonly located along with heater element 70 in a valve block 72.As explained above, air dryer 16 includes temperature sensor 50 fordetermining the approximate temperature of valve block 72 and thus drainvalve 24, inlet valves 42 and 44, and outlet valves 52 and 54.Temperature sensor 76 is shown as being positioned to detect thetemperature of air passing through air dryer 16, but may be positionedto detect the temperature of valve block 72, the temperature of theinlet air, the temperature of ambient air, or some combination of theabove.

Referring to FIG. 4, air dryer controller 40 is programmed to implementa heater control process 80 to ensure that valve block 72 issufficiently heated to a temperature that avoids the likelihood thatdrain valve 24, inlet valves 42 and 44, or outlet valves 52 and 54 canbecome frozen. First, controller 40 reads the temperature 82 such as byusing temperature 76 positioned in valve block 72. Next, a check 84 isperformed to determine whether the temperature is below freezing (or anyother predetermined temperature selected to be indicative of a risk thatdrain valve 24, inlet valves 42 and 44, or outlet valves 52 and 54 willbecome frozen). If the temperature is below the threshold at check 82,controller 40 inhibits valve operation 86, such as by inhibiting theoperation of drain valve 24, inlet valves 42 and 44, and/or outletvalves 52 and 54 until such time as the temperature has risen above thethreshold. Thus, if air dryer 16 is turned on after an extended coldsoak at low temperature, controller 40 will affirmatively inhibitactuation of drain valve 24, inlet valves 42 and 44, and/or outletvalves 52 and 54 until heater element 70 has warmed valve block 72sufficiently to prevent any of drain valve 24, inlet valves 42 and 44,and outlet valves 52 and 54 from freezing in an open position andcausing an undesired venting of compressed air from locomotive airsupply system 10. Preferably, inlet valves 42 and 44 are normally openand exhaust valves 52 and 54 are normally closed in the unpowered state,so that compressed air may flow through air dryer 16 to MR2 when allvalves are in an unpowered state. By using closed loop temperaturefeedback to control inhibit the operation of the series of valves, thestart-up time for a cold air dryer is proportional to the startingtemperature. Alternatively, a simple system which uses a fixed timedelay calculated to allow the valve block to warm to above freezing forthe worst case condition may be provided.

The same sensor and controller may be used to turn off the heater, whenthe temperature of the valve block is at or above the targettemperature, thus regulating the temperature of the valve block to atemperature above freezing when the ambient temperature is belowfreezing; and turning the heater off completely when the ambienttemperature, as indicated by the temperature of the valve block, isabove freezing.

What is claimed is:
 1. An air dryer, comprising; an inlet coupled to amain reservoir of a locomotive for receiving compressed air from themain reservoir of the locomotive; a series of valves positioned in avalve block for controlling the movement of the compressed air through adesiccant; a heater configured to warm the valve block; a temperaturesensor for outputting a signal indicating the temperature of at least aportion of the air dryer; and a controller piloting the series of valvesthat is programmed to prevent the series of valves from opening untilthe signal received from the temperature sensor indicates that theseries of valves will not freeze when operated.
 2. The air dryer ofclaim 1, wherein the series of valves includes a pair of inlet valvesand a pair of outlet valves.
 3. The air dryer of claim 2, wherein thetemperature sensor is positioned to determine the temperature of airflowing through the air dryer.
 4. The air dryer of claim 2, wherein thetemperature sensor is positioned to determine the temperature of thevalve block housing the series of valves.
 5. A method of preventingfrozen air dryer valves, comprising the steps of: providing an air dryerhaving an inlet for receiving compressed air, a series of valvespositioned in a valve block for controlling the movement of thecompressed air through a desiccant, a heater configured to warm thevalve block, a temperature sensor for outputting a signal indicating thetemperature of at least a portion of the air dryer, a controllerpiloting the series of valves; coupling the inlet of the air dryer to amain reservoir of a locomotive to receive compressed air from the mainreservoir of the locomotive; receiving the signal indicating thetemperature in the air dryer from the temperature sensor; and preventingthe series of valves from opening if the signal received from thetemperature sensor indicates that any of the series of valves couldfreeze when opened.
 6. The method of claim 5, wherein the series ofvalves includes a pair of inlet valves and a pair of outlet valves.